There are different types of loupes for surgical, medical and dental applications, including frame-mounted and flip-up styles and through-the-lens (TTL) loupes. Making reference to FIG. 1, the declination angle of loupes may be defined as the angle 114 between a reference line 104 connecting the top of the ears 117 (where the frame arm rests) to the corner of the eyes, and the optical axis 106 of the loupe oculars. The frame temple arm 120 may be used as the reference line if the temple arms are mounted at the same level with eyes (keeping in mind that the temple arms of some frames are higher than eye level).
While it is relatively easy to increase declination angle with “flip-up” loupes because the oculars do not need the eyeglass lenses for support, the positioning of existing TTL oculars is limited by the bottom edge of each lens 122. As such, a significant problem with TTL loupes is the relatively small declination angle due to the limitation of size of the carrier lens. This causes the user to bend their head downwardly from the horizontal 102 at a head angle of 112 (or greater), which may result in neck strain. Thus, any technique to increase the declination angle in TTL loupes would result in a more ergonomic design.